The goal of this proposal is to understand the inhibitory mechanism of IKKalpha in IKKalpha-mediated tumor development in skin carcinogenesis. Our recent results showed that Ikkalpha+/- mice developed twice more benign tumors, papillomas, and ten times more malignant carcinomas than Ikkalpha+/+ mice did in skin carcinogenesis. The patterns and levels of IKKalpha expression were well-correlated to stages of tumor development. Importantly, Ikkalpha+/- carcinomas lost the wildtype allele. Regardless of Ikkalpha genotypes, poorly differentiated carcinomas lost IKKalpha, indicating that loss of IKKalpha is associated with tumor formation and malignant carcinoma development in skin carcinogenesis. To investigate whether the increased expression of IKKalpha inhibits tumor development, we generated epidermis-specific IKKalpha transgenic mice. Our preliminary results showed that these mice were resistant to tumor progression. To investigate the mechanism of the IKKalpha inhibitory function on tumor development, we plan to: 1) Determine the inhibitory effect of IKKalpha on tumor development by using transgenic mice expressing different forms of IKKalpha in epidermis. To determine the mechanism of the inhibitory effect of IKKalpha on tumor development, we will generate the transgenic mice expressing the kinase inactive (KA) and the C-terminal deletion (C80, a stronger differentiation ability) forms of IKKalpha and determine their abilities in repressing tumor development by using the two-step and complete skin carcinogenesis protocols. 2) Determine the mechanisms of the inhibitory effect of IKKalpha on tumor development. Based on our findings, the mechanisms of IKKalpha-mediated tumor development includes the elevated mitogenic activity, such as Erk, TGFalpha, EGF, VEGF-A, IL-1alpha and TNFalpha, and the genomic instability, such as deregulating expression of multiple genes, including nucleophosmin (NPM) and 14-3-3sigma that are involved in chromosome duplication, DNA repair, and cell cycle control. We will determine whether overexpressed IKKalpha in skin regulates these elements or other IKKalpha target genes to inhibit tumor development. In addition, we will investigate how tumor cells bypass IKKalpha to develop carcinomas, because IKKalpha transgenic mice still developed some malignant carcinomas. This proposed study will further provide an outline of the inhibitory mechanism of IKKalpha and evaluate whether IKKalpha can be a potential candidate for preventing skin tumor development.